Bimetallic tube in a heat exchanger of an ice making machine

ABSTRACT

A heat exchanger tube in a heat exchanger for an ice making machine includes a bimetallic heat exchanger tube to improve capacity and wear characteristics of the heat exchanger. The heat exchanger tube has an outer portion with a first material composition and an inner portion with a second material composition where the first material composition is different from the second material composition. The first material composition is compatible with the refrigerants used in the heat exchanger unit of the ice making machine. The second material composition is compatible with the feed solution being chilled in the heat exchanger tube.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to heat exchanger tubes for heatexchangers used in chilling fluids or making ice. Specifically, theinvention relates to an improvement in the heat exchangers where abimetallic heat exchanger tube is used to increase the capacity of theheat exchanger and lower the rate of wear of other parts within the heatexchanger.

[0003] 2. Description of the Related Art

[0004] Heat exchangers for making a chilled fluid or water-ice mixtureare well known in the art. These heat exchangers are used in a varietyof industries including the food processing industry where a slurry icemixture is used to refrigerate meats, produce, and fish. The heatexchangers are also used in the processing of milk products andconcentrated fruit juices, and in HVAC and brewing applications. Inthese heat exchangers, the ice water mixture is pumped through heatexchanger tubes and refrigerant is circulated around the tubes. Thefluid mixture is chilled as it passes through the heat exchanger tubes,and the chilled mixture is pooled in a reservoir where it may beaccumulated for further processing, as required. In order to prevent icefrom forming in the tube and adhering to the tube, mechanical agitatorsare used to maintain the flow of the chilled mixture through the heatexchanger.

[0005] One machine that has gained wide use in the food processingindustry is a whip rod heat exchanger. A typical whip rod heat exchangerhas vertical heat transfer tubes with whip rods positioned in the heattransfer tubes. Feed or process solution is directed into the tubes. Adrive mechanism in the heat exchanger develops relative motion betweenthe tubes and the whip rods to distribute the feed solution evenlywithin the tube, thus more effectively freezing or chilling the feedsolution. An orbital tube evaporator system is described in U.S. Pat.No. 5,221,439, issued Jun. 22, 1993, and entitled Orbital TubeEvaporator With Improved Heat Transfer. An improvement to that apparatusis described in U.S. Pat. No. 5,385,645, issued Jan. 31, 1995, andentitled Heat Transfer Apparatus with Positive Drive Orbital Whip Rod,the disclosures of which are incorporated herein by reference. In theorbital whip rod system described in the '645 patent, the feed solutionis pumped through the vertical tubes and chilled by the refrigerantcirculating in the chamber surrounding the vertical heat exchangertubes. The whip rod moves in an orbital direction inside a stationaryheat exchanger tube so that the fluid is distributed as a film on theinner diameter surface of the tube. The whip rod creates a turbulentflow liquid layer that prevents the feed solution from sticking to theinner wall of the tube as it is chilled and moves from the top of theheat exchanger to the bottom of the heat exchanger. The refrigerant iscirculated around the outside of the heat transfer tube to remove heatfrom the feed solution to chill the feed solution. The chilled feedsolution may then be directed from the bottom of the vertical tubes to astorage tank where it may be pumped away or otherwise utilized asrequired by the application.

[0006] An improvement to the orbital whip rod heat exchanger isdescribed in U.S. Pat. No. 5,953,924, issued Sep. 21, 1999, and entitledApparatus, Process and System for Tube and Whip Rod Heat Exchanger, thedisclosure of which is incorporated herein by reference. The '924 patentdescribes an invention where the orbital whip rod heat exchanger may beconfigured to operate in a flooded tube mode where the heat exchangertubes are flooded with process fluid and the whip rod is driven fromboth ends of the heat exchanger tube, and a falling film mode, where theheat exchanger tube is partially filled with process fluid and the whiprod is suspended in the tube and driven from a drive plate above thetube.

[0007] Another style of heat exchanger for producing an ice-slurrymixture found in wide spread use in the food processing industry is aheat exchanger with flooded refrigerated tubes having a rotating bladeinside the tube. These heat exchangers are described in U.S. Pat. No.5,884,501 issued Mar. 23, 1999, and U.S. Pat. No. 6,056,046, issued May2, 2000, the disclosures of which are hereby incorporated by reference.The ice slurry mixture is formed in a central tube in a heat exchangerhousing and is moved from an inlet to an outlet in the central tube by arotating blade. Refrigerant is circulated in refrigerant tubes formedaround the outer periphery of the heat exchanger housing. The rotatingblades move past the inner wall of the central tube of the heatexchanger without contacting it and thereby move cooled fluid from thesurface to prevent the deposition of ice crystals on the inner wall ofthe heat exchanger.

[0008] In these conventional heat exchangers, including the orbital whiprod heat exchanger, the tubes are generally made from stainless steelsince stainless steel is both corrosion resistant to the feed solutionbeing pumped through the inner wall surfaces of the tube and therefrigerant which circulates around the outer wall surfaces of the heatexchanger tube. Stainless steel also has good thermal conductivity andgood strength. In stainless steel tube heat exchangers, HCFC and ammoniamay be used as refrigerants in a variety of applications where thechilled feed solutions may include seawater and food products. Copperhas also been used for constructing the heat exchanger tubes; however,copper is generally not compatible with ammonia based refrigerantsystems. In industries where there is a higher concern for safety, HCFCrefrigerants continue to be used. On the other hand, in process coolingapplications, ammonia based refrigerants are well suited because oftheir low cost and high efficiency. As stainless steel tubes can be usedin both the systems, stainless steel heat exchanger tube systems arecommon.

[0009] However, stainless steel heat exchanger tube systems have manydisadvantages. Stainless steel tube heat exchangers are generally moreexpensive when compared to copper tube heat exchangers. In theconstruction of copper tube or stainless steel tube heat exchangers, thetubes are generally roll fastened to the tube sheet. The tube to tubesheet connection must be a leak tight boundary to prevent therefrigerant from leaking out of the heat exchanger unit and into thefeed solution and possibly the surrounding workspaces. Since ammonia istoxic, in some applications that use ammonia as a refrigerant, thestainless steel tube must be welded to the tube sheet in addition tobeing roll fastened to ensure the required leak tight boundary for theapplication. Since copper tube exchangers do not use ammonia, the tubeto tube sheet connection need only be roll fastened, thus loweringmanufacturing cost. Stainless steel also generally has a higher materialcost than copper.

[0010] In these types of heat exchangers, seamless stainless steel tubeis preferred. A welded tube may also be used if the weld bead isflattened to provide a smooth transition over the seam. In the orbitalrod heat exchanger, the smooth inner surface of the tube allows the whiprod to travel along the inner surface without “bumping” or jumping overthe seam. The consistent motion of the whip rod creates the turbulentflow layer needed to prevent ice formation in the tube. In the bladetype heat exchanger, the smooth surface is required so that the smallradial clearance between the blades and the inner surface of the tube ismaintained for fluid flow along the inner surface of the tube. A morecostly seamless tube or the secondary operation of flattening the weldbead is an added expense. Since copper tubes are usually drawn without aseam when manufactured, they are generally less expensive than seamlessstainless steel tubing.

[0011] Stainless steel heat exchanger tubes also have other drawbackswhen compared to conventional copper-based systems. In order to depressthe freezing point of solution as it is processed and promote theformation of ice slurry, additives such as ethylene glycol, propyleneglycol, urea, and ethanol may be added. These substances when used inthe feed solution cause the ice crystals of the feed solution to form assmall flakes or as powdery solids rather than large, flat flaky crystalstructures. The powdery consistency of the ice particles prevents thefeed solution from adhering to the inner wall surfaces of the heatexchanger tube. Other corrosion inhibiting substances such asdi-potassium phosphate (K₂ HPO₄) are also commonly added.

[0012] Although the additives enhance the formation of the ice slurrymixture in the tubes, the use of these additives in the feed solutiontends to accelerate corrosion and wear of components in the heatexchanger. Specifically, the eccentrics and tube inserts in the drivemechanism for positioning and driving the whip rod in the tube are madefrom hardened steel materials. This difference in materials in thepresence of the feed solution accelerates corrosive attack on thesedrive components. In an orbital rod heat exchanger having a stainlesssteel tube construction, the tube inserts and eccentrics are mostanodic. Because these parts generally have a small surface area, theyare highly susceptible to galvanic corrosion. As tube inserts andeccentrics corrode, their surfaces grow rough, and the hardened,roughened surfaces contribute to accelerated wear of the othercomponents in the drive mechanism such as the plastic counter crank,plastic sleeve bearing, and whip rod.

[0013] The attack tends to be more acute when the concentration ofcorrosion inhibiting agents in the feed solution is low. To slow thecorrosion, the concentration of the additives must be maintainedrelatively high. Generally, phosphate must be maintained at a level ofat least 1000 ppm, and preferably 4000 ppm, in order to preventcorrosion. The level of additives must be periodically monitored toprevent deterioration of the system. Additionally, certain areas in thedrive system experience a combination of corrosion and erosion fromsuspended solids in the feed solution. In order to prevent this type ofrapid wear, secondary filtration system are commonly installed on icemaking machines with stainless steel heat exchanger tubes. This alsoadds cost to the machine.

[0014] In addition to the higher manufacturing costs and wear problemsfound with stainless steel tube heat exchangers, ice making machinesusing stainless steel tubes generally have a lower ice making capacitywhen compared to ice making machines with heat exchangers using coppertubes.

SUMMARY OF THE INVENTION

[0015] In order to solve these and other problems in the prior art, theinventor has succeeded in designing a heat exchanger tube that is animprovement to the heat exchanger tubes of the prior art. The heatexchanger tube of the present invention increases the capacity of icemaking machines using stainless steel heat exchanger tubes and improvesthe wear characteristics of other components in the heat exchanger. Thepresent invention is an improvement to the heat exchanger tubes used inconventional ice making machines that produce an ice-water slurrymixture. The heat exchanger tube has an outer portion that is formedfrom a first material composition, and an inner portion that is formedfrom a second material composition. The outer and inner portions of theheat exchanger tube are integrally joined to create a one-piece tube.The outer portion of the tube may be made from a carbon steel,austenitic stainless steel, martensitic stainless steel, or aluminum.The inner portion of the tube may be made from copper, copper-nickel, orbrass materials, depending on the feed solution being processed in theheat exchanger. The outer portion of the tube is compatible with a widerange of refrigerants, and the inner portion permits a higher heat fluxthrough the heat exchanger tubes to increase the capacity of theice-making machine.

[0016] The heat exchanger tube of the present invention may be used in awide variety of heat exchangers including a whip rod heat exchanger.When the heat exchanger tube is installed in a whip rod heat exchanger,the inner portion of the heat exchanger tube is preferably seamless toallow smooth relative motion between the whip rod and the heat exchangertube. Additionally, the inner portion of the heat exchanger tubepreferably has a low galvanic potential when compared to othercomponents in the heat exchanger when these components are in thepresence of the feed solution. This allows the inner portion of the heatexchanger tube to act as a sacrificial anode with the other componentsin the heat exchanger, specifically the drive components which producethe orbital relative motion between the tube and whip rod, to preventcorrosion of these components and reduce wear.

[0017] In forming the heat exchanger tube of the present invention, theouter portion of the heat exchanger tube preferably takes the form of anouter cylindrical sleeve and the inner portion takes the form of aninner cylindrical sleeve. The inner cylindrical sleeve is fitted withinthe bore of the outer cylindrical sleeve. The outer cylindrical sleevemay be drawn over the inner cylindrical sleeve such that the two sleevesare joined together by a mechanical interference fit. A third thermallyconductive material, such as a thermal mastic or grease, may be used todecrease the thermal resistance between the inner and outer cylindricalsleeves.

[0018] The outer cylindrical sleeve may also take the form of a claddingthat is wrapped around the inner cylindrical sleeve such that the outerdiameter surface of the inner cylindrical sleeve is substantiallycovered by the outer cladding. In this arrangement, the outercylindrical sleeve may be formed by rolling a flat stock material aroundthe outer diameter surface of the inner cylindrical sleeve. A thirdmaterial, such as a brazing material or other compound capable ofjoining the outer and inner cylindrical sleeves, may be interposedbetween the inner and outer sleeves and in the area between the two endsof the rolled flat stock material to form a metallurgical bond betweenthe outer cladding and the inner sleeve. Similarly, the innercylindrical sleeve may be formed from an inner cladding that is appliedto the bore of the outer cylindrical sleeve. The outer or inner claddingmay also take the form of a coating attached to the respective inner orouter diameter surfaces of the heat exchanger tube through anelectrochemical, flame spray, or plasma coating process. In each casethe cladding layer and tube are compatible with the refrigerant or feedsolution being used in the heat exchanger, and the thermal resistancebetween the cladding layer and the tube is minimized.

[0019] While the principal advantages and features of certain specificsof the preferred embodiments have been explained above, a greaterunderstanding of the invention may be obtained by referring to thedrawings and detailed description of the preferred embodiment whichfollow.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0020]FIG. 1 is a partial, perspective view of a typical heat exchangerin which the heat exchanger tube of the present invention is used;

[0021]FIG. 2 is a partial, front elevational view of the heat exchangertube of FIG. 1;

[0022]FIG. 3 is a cross-sectional view of the heat exchanger tubeattached to a tube sheet of the heat exchanger;

[0023]FIG. 4 is an alternate embodiment of FIG. 3 showing the heatexchanger tube attached to the tube sheet of the heat exchanger;

[0024]FIG. 5 is an alternative embodiment of FIG. 4 showing the heatexchanger tube attached to the tube sheet of the heat exchanger;

[0025]FIG. 6 is an alternative embodiment of FIG. 4 showing the heatexchanger tube attached to the tube sheet of the heat exchanger; and

[0026]FIG. 7 is an alternative embodiment of FIG. 4 showing the heatexchanger tube attached to the tube sheet of the heat exchanger.

[0027] Corresponding reference characters indicate corresponding partthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] The bimetallic tube 10 of the present invention is used in a heatexchanger 12, such as the orbital whip rod freezer shown in FIG. 1. Itshould be understood that the orbital rod freezer is one type of icemaking machine to which the present invention may be applied. Thebimetallic tube 10 of the present invention may also be used in the heatexchanger units of other ice making machines as an improvement to thecapacity and wear characteristics of the heat exchanger unit. As shownin FIG. 1, the heat exchanger unit 12 of the orbital whip rod freezerhas several drive components 13 including a drive plate 14 having aplurality of drive holes 16 which are matched to interfit with aplurality of drive pins 18. Each of the drive pins 18 is connected to acounter crank 20 and the counter crank 20 has a feed orifice 22 and awhip rod hole 24 through which a whip rod 26 is supported by an annularflange 28 at its upper end. Each whip rod 26 is inserted into the heatexchanger tube 10. The tubes 10 are held in place and fixed in a spacedrelationship by an upper and lower tube sheet 30,32. The feed solutionflows through the drive holes 16 in the drive plate 14 and onto the topof the counter crank 20 where the liquid accumulates before it entersthrough the feed orifice hole 22 and into the interior of the heatexchanger tube 10. The direction of flow of the feed solution isindicated at reference numerals 33. As the whip rod 26 is driven in anorbital motion around the interior of the tube 10, the whip rod 26spreads the feed solution in a thin film around the interior of the heatexchanger tube 10 to enhance chilling of the feed solution. Arefrigerant is circulated in an interior space 34 between the tubesheets 30,32 and around the exterior surfaces of the tubes 10. Therefrigerant removes heat from the feed solution, chilling the solutionso that as the solution flows through the tubes 10, an ice-water mixtureor slurry exits the bottom of the tubes 10.

[0029]FIG. 2 provides greater detail of the heat exchanger tube 10 ofthe present invention. The tube 10 is arranged in the heat exchangerwhere the refrigerant circulates around an outer wall surface 36 of thetube 10 and the feed solution flows through an inner wall surface 38 ofthe tube. The tube 10 has an outer portion 40 which forms the outer wallsurface 36 and has a first material composition. The tube 10 has aninner portion 42 which forms the inner wall surface 38 of the tube 10and has a second material composition. The first material composition ofthe outer portion 40 of the heat exchanger tube is different from thesecond material composition of the inner portion 42.

[0030] In the preferred embodiment of the invention, the first materialcomposition of the outer portion 40 of the heat exchanger tube 10preferably resists corrosion by the refrigerant and provides sufficientthermal conductivity through the wall of the heat exchanger tube 10. Thesecond material composition of the inner portion 42 of the heatexchanger tube also has good thermal conductivity properties while beingcompatible with the feed solution of the particular application of theheat exchanger 12. The inner portion 42 also reduces corrosive attack onother drive components 13 when the feed solution is present in the heatexchanger 12.

[0031] In the preferred embodiment of the heat exchanger tube 10, theouter portion 40 is preferably made from an austenitic 304 stainlesssteel material. Carbon steel and aluminum are also suitable materialssince they are compatible with ammonia based refrigerants. Martensiticstainless steels such as AISI 410 or AISI 420 may also be used to formthe outer portion 40 of the heat exchanger tube 10. When constructingthe inner portion 42 of the heat exchanger tube 10, copper based alloyssuch as copper 122, or copper 194 may be used. Additionally, coppernickel alloys may be used as copper nickel alloys have a superiorcorrosion resistance to sea water. Copper nickel 706 has been found tobe an acceptable material in this particular type of application. Leadedbrass and other brass materials have also been found to be suitable forforming the inner portion of the heat exchanger tube. Specifically,brass 330 and brass 270 generally have good resistance to oxidation inindustrial, rural, and marine atmospheres.

[0032] As shown in FIG. 2, the outer portion 40 of the heat exchangertube is formed as an outer cylindrical sleeve 44, and the inner portion42 is formed as an inner cylindrical sleeve 46. The inner cylindricalsleeve 46 is fitted within the bore of the outer cylindrical sleeve 44.Thus, the heat exchanger tube 10 may take the form of a first, outertube or pipe with a second, inner tube or pipe fitted concentricallywithin the bore of the first, outer tube or pipe. To minimize materialcosts of forming the tube 10, the outer cylindrical sleeve 44 may takethe form of a welded tube while the inner cylindrical sleeve 46 may takethe form of drawn tube. The drawn tube is preferred since it willprovide a smooth surface on the inner wall 38 of the heat exchanger tube10. The smooth surface provides consistent motion for the whip rod andeven dispersion of the feed solution to prevent ice formation on theinner walls of the tube. Preferably, the tube 10 is made by drawing theinner cylindrical sleeve 46 through the bore of the outer cylindricalsleeve 44 thus attaching the sleeves 44,46 by a mechanical interferencefit. For a tube 10 having an outer diameter of 1½ inches, a tube wall ofbetween 0.035″-0.065″ inches is preferred. In this construction, each ofthe tube walls of both the inner and outer cylindrical sleeves 44,46 isapproximately {fraction (1/64)} inches to {fraction (1/32)} inchesthick. In a typical orbital whip rod heat exchanger, the heat exchangertube measuring 1½ inches on its outer diameter is generally four feetlong.

[0033]FIGS. 3 through 7 show preferred methods of attaching the tube 10to the upper tube sheet 30 of the heat exchanger 12. Although not shownin the Figures, this method is also used on the lower tube sheet 32.Depending upon the application, the tube 10 may be rolled into a tubehole 47 in the tube sheets 30,32 using common practices in the art.Generally, the roll attachment or roll fastening 48 as shown in FIG. 3provides a leak tight boundary between the refrigerant and the feedsolution. Depending upon the application, a welded or brazed joint 50may also be used in conjunction with a roll fastened connection 48. FIG.4 shows the roll fastened tube to tube sheet connection 48 and thebrazed connection 50. The brazed connection 50 secures and protects theouter cylindrical sleeve 44 from corrosive attack from the feed solutionor the additives that may be present in the feed solution. For instance,brazing may be used to protect the exposed end of a carbon steel outercylindrical sleeve 44 from corrosion by the glycol solution that may beadded to the feed solution to promote slurry formation. The heatexchanger tube may also be welded to the tube sheets 30,32. However,this process is costly as each tube in the heat exchanger must be weldedindividually. Since brazing can be done in a batch operation such as ina furnace brazing operation, brazing the heat exchanger tube 10 providesan inexpensive way to protect exposed ends of the heat exchanger tube 10while providing the necessary leak protection found in welding.

[0034]FIGS. 5, 6, and 7 show alternative methods of attaching the tube10 to the tube sheet 30. In each of these arrangements, the outercylindrical sleeve 44 is cut back from the distal end of the tube 10approximately {fraction (3/16)} inches to ⅜ inches to expose the outerdiameter surface of the inner cylindrical sleeve 46. Cutting back theouter cylindrical sleeve 44 in this manner forms an annular groove 52 onthe distal end of the tube 10 between the inner cylindrical sleeve 46and the tube hole 47. In FIG. 5, the brazing material or weld material50 is deposited in the annular groove 52 where it covers the exposed endof the outer cylindrical sleeve 44 and bonds the tube 10 to the tubesheet 30. FIG. 6 shows a similar arrangement of the outer cylindricalsleeve 44. In this case, the distal end of the inner cylindrical sleeve46 is peened over the exposed end of the outer cylindrical sleeve 44 tocover the exposed end of the outer cylindrical sleeve 44. The weldmaterial 50 is then deposited between the tube sheet 30 and the peenedover portion of the inner cylindrical sleeve 46. FIG. 7 shows analternate method of covering the exposed end of the outer cylindricalsleeve 44 where the inner cylindrical sleeve 46 is peened over theexposed end of the outer cylindrical sleeve 44 to form a seal with theinside surface of the tube hole 47.

[0035] The bimetallic tube 10 of the present operation provides asubstantial increase in capacity while reducing wear of drive systemcomponents. By using copper as a material for the inner cylindricalsleeve 46, the heat exchanger 12 has a higher capacity than heatexchangers using stainless steel tubes. Additionally, the innercylindrical sleeve 46 acts as a sacrificial anode in the presence of thefeed solution with the hardened steel materials that are used tofabricate the drive components 13 of the heat exchanger 12. Thisprevents corrosive attack on the hardened steel drive components 13 andpromotes longer life. This increase in wear life may be achieved byusing less or no additional additives to the feed solution. With theouter cylindrical sleeve 44 constructed from the stainless steel, a widevariety of refrigerants can be used in the heat exchanger 12. As steeland stainless steel are both resistant to corrosion in the presence ofammonia, low temperature cooling may be achieved. Because the outercylindrical sleeve 44 does not form the inner diameter surface of theheat exchanger tube and does not contact the whip rod 26, the outercylindrical sleeve 44 may be made from less expensive forms of material,such as a welded tube.

[0036] In an alternative embodiment of the invention, the outercylindrical sleeve may be formed from a tube shaped member thatsubstantially covers the outer diameter surface of the inner cylindricalsleeve. In this embodiment, the outer cylindrical sleeve may be formedby rolling sheet stock material around the outer diameter surface of theinner cylindrical sleeve and joining the sheet material to the outercylindrical sleeve through a welding or brazing process. The ends of thesheet stock may also be coated and joined together to form a seam on theouter diameter surface of the inner cylindrical sleeve through the samewelding or brazing process. The outer, tube shaped member may also beformed by a plating process such as electrochemical deposition or plasmaspray. The inner cylindrical sleeve may be formed in similar ways usinga cladding material of a different material composition than the outercylindrical sleeve. The inner cladding may also be formed from a platingprocess such as electrochemical deposition or plasma spray. The primaryconsiderations for forming the cladding layer on the inner diametersurface of the outer cylindrical sleeve is to provide a surface whichprevents ice particles from adhering to the surface of the tube and toallow smooth relative motion between the whip rod or other mechanicalagitation means positioned in the heat exchanger tube.

[0037] In another embodiment of the invention, a third material may beused between the inner and outer sleeves of the heat exchanger tube tolower thermal resistance between the outer and inner sleeves. The thirdmaterial may be a thermal mastic or grease that is applied to thesurfaces of one of the sleeves of the heat exchanger tube. During theprocess of drawing the inner and outer sleeve into the heat exchangertube, a layer of grease or thermal mastic is placed between the contactsurfaces of the inner and outer sleeves. The grease or thermal masticexcludes air and reduces the contact resistance to heat transfer betweenthe inner and outer sleeves. Excess grease or mastic may then beextruded out of the tube as the tube is pulled though the draw bench.The third material may also be a brazing material or solder. A brazingmaterial or solder material forms a metallurgical bond between inner andouter sleeves after the tube is heated to the proper temperature. Themetallurgical bond also reduces thermal resistance between the inner andouter sleeves of the heat exchanger tube. Although use of the thirdmaterial is more costly when compared to the previously described drawoperation which produces the mechanical interference fit, the thirdmaterial increases the integrity of the heat exchanger tube anddecreases the thermal resistance between the inner and outer sleeves, asmay be desired in some applications.

[0038] Although the embodiments of the present invention have beendescribed with reference to an orbital whip rod heat exchanger, itshould be understood that the present invention may be applied tovarious other heat exchangers used to chill feed solutions flowingthrough the interior of a heat exchanger tube. This invention may alsobe applied to other heat exchangers that use scouring blades in acylindrical chamber to produce a pumpable ice-water mixture.

[0039] As various changes could be made in the above constructionwithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not inany limiting sense. The invention therefore shall solely be limited bythe scope of the claims set forth below, and their legal equivalents.

What is claimed is:
 1. In an ice making machine for producing an iceslurry mixture in which the ice slurry mixture flows through at leastone heat exchanger tube in a heat exchanger of the ice making machine,the improvement comprising: an outer portion of the heat exchanger tubehaving a first material composition and an inner portion of the heatexchanger tube having a second material composition, the first materialcomposition being different from the second material composition, theouter portion and inner portion of the tube being integrally joined toform the heat exchanger tube.
 2. The ice making machine of claim 1,wherein: the outer portion of the tube is an outer cylindrical sleeveand the inner portion of the tube is an inner cylindrical sleeve, eachof the outer and inner cylindrical sleeves has an outer diameter surfaceand an inner diameter surface, the outer diameter surface of the outercylindrical sleeve forms an exterior of the heat exchanger tube, theinner diameter surface of the inner cylindrical sleeve forms an interiorof the heat exchanger tube, the outer cylindrical sleeve surrounds theinner cylindrical sleeve whereby the inner diameter surface of the outercylindrical sleeve is in contact with the outer diameter surface of theinner cylindrical sleeve.
 3. The ice making machine of claim 2, wherein:the outer sleeve is a welded tube.
 4. The ice making machine of claim 2,wherein: the inner sleeve is a drawn tube.
 5. The ice making machine ofclaim 1, wherein: the first material composition is one from the groupconsisting of carbon steel, austenitic stainless steel, martensiticstainless steel, and aluminum.
 6. The ice making machine of claim 1,wherein: the second material composition is a copper based material. 7.The ice making machine of claim 2, wherein: the inner sleeve and theouter sleeve are joined by a mechanical interference fit.
 8. The icemaking machine of claim 2, further comprising: a third materialinterposed between the inner and outer sleeve, the third materialmetallurgically bonding the inner and outer sleeves.
 9. The ice makingmachine of claim 2, further comprising: a thermal mastic interposedbetween the inner and outer sleeve, whereby the thermal mastic increasesheat transfer between the inner and outer sleeves.
 10. A whip rod heatexchanger comprising: a heat exchanger being adapted to chill a feedsolution to form a crystallized solid-liquid mixture of the feedsolution; and at least one heat exchanger tube in the heat exchangerhaving a bore to contain the feed solution therein and at least one whiprod having relative motion with the heat exchanger tube whereby the whiprod distributes feed solution within the heat exchanger tube, the innerdiameter surface of the heat exchanger tube being covered with an innercladding, the inner cladding having a material composition differentfrom a material composition of the tube, the inner claddingsubstantially covering the inner diameter surface of the tube wherebythe inner cladding is in contact with the feed solution and defines apath of solution flow through the tube.
 11. The heat exchanger of claim10, wherein: the inner cladding is a copper based metal.
 12. The heatexchanger of claim 11, wherein: the inner cladding is hollow andcylindrically shaped, the inner cladding is mechanically joined to thetube.
 13. The heat exchanger of claim 10, wherein: the heat exchangertube is made from one of the group consisting of austenitic stainlesssteel, martensitic stainless, carbon steel, and aluminum.
 14. The heatexchanger of claim 10, wherein: the inner cladding is seamless.
 15. Theheat exchanger of claim 10, wherein: the inner cladding acts as asacrificial anode when feed solution is introduced to the heatexchanger.
 16. The heat exchanger of claim 10, wherein: the innercladding is a seamless tube; and the heat exchanger tube is atube-shaped member joined to the inner cladding.
 17. The heat exchangerof claim 16, wherein: the tube-shaped member is mechanically joined tothe inner cladding.
 18. The heat exchanger of claim 16, wherein: thetube-shaped member is bonded to the inner cladding.
 19. The heatexchanger of claim 16, wherein: a third material is interposed among thetube-shaped member and the inner cladding and joins the tube-shapedmember to the inner cladding.
 20. The heat exchanger of claim 16,wherein: the tube-shaped member is compatible with ammonia and ammoniumcompounds.
 21. The heat exchanger of claim 10, wherein: the heatexchanger has a tube sheet that holds the heat exchanger tubes withinthe heat exchanger and directs the feed solution to flow in the heatexchanger through the heat exchanger tubes, each of the tubes isconnected to the tube sheet by roll fastening and brazing.
 22. A heatexchanger tube for a heat exchanger in an ice slurry generating machine,the heat exchanger tube comprising: a first, inner surface made from afirst material composition, and a second outer surface made from asecond material composition, the first material composition beingdifferent then the second material composition.
 23. The heat exchangertube of claim 22, wherein: the tube is comprised of two concentricsleeves.
 24. The heat exchanger tube of claim 23, wherein: the tube isformed by drawing an outer sleeve over an inner sleeve.
 25. The heatexchanger tube of claim 23, wherein: the tube is comprised of an outersleeve over an inner sleeve.
 26. The heat exchanger tube of claim 23,wherein: the sleeves are interference fit to each other.
 27. The heatexchanger tube of claim 23, wherein: substantially the entirety of theinner sleeve is surrounded by the outer sleeve.
 28. The heat exchangertube of claim 23, wherein: substantially the entirety of the adjacentsleeve surfaces are in physical contact.
 29. The heat exchanger tube ofclaim 23, wherein: the inner surface of the inner sleeve issubstantially seamless.
 30. The heat exchanger tube of claim 23,wherein: the tube has a third material interposed among the inner andouter sleeves, the third material bonds the inner and outer sleevestogether.
 31. The heat exchanger tube of claim 23, wherein: the tube hasa third material interposed between the inner and outer sleeves, thethird material is a thermal mastic.
 32. The heat exchanger tube of claim23, wherein: the first material composition is a copper based material.33. The heat exchanger tube of claim 23, wherein: the second materialcomposition is one from the group consisting of carbon steel, austeniticstainless steel, martensitic stainless steel, and aluminum.
 34. A heatexchanger tube for an ice slurry generator comprising: a first innersurface and a second outer surface, the first inner surface beingadapted to contact a feed solution and having a galvanic property to actas a sacrificial anode in the presence of the feed solution.
 35. Theheat exchanger tube of claim 34, wherein: each of the inner surfaces andouter surfaces comprise sleeves.
 36. A method for increasing thecapacity of an ice making machine wherein the ice making machine has aheat exchanger with a heat exchanger tube, an ice slurry mixture flowsin the heat exchanger tube and refrigerant is circulated in a chamber inthe heat exchanger, the heat exchanger tube has an inlet and an outletand means for moving the ice slurry mixture in the tube between theinlet and the outlet, the method comprising: providing the heatexchanger tube with an inner portion of the heat exchanger tube formedfrom a first material composition and an outer portion of the heatexchanger tube formed from a second material composition, the firstmaterial composition being different from the second materialcomposition whereby the inner and outer portions of the tube are joinedsuch that the thermal resistance between the inner and outer portions isminimized and the inner portion limits the ice slurry mixture fromadhering to the heat exchanger tube.
 37. The method of claim 36, whereinthe step of providing the heat exchanger tube includes: providing theouter portion of the tube in the form of an outer cylindrical sleeve andthe inner portion of the tube in the form of an inner cylindrical sleevewhereby each of the outer and inner cylindrical sleeves has an outerdiameter surface and an inner diameter surface and the outer diametersurface of the outer cylindrical sleeve forms an exterior of the heatexchanger tube and the inner diameter surface of the inner cylindricalsleeve forms an interior of the heat exchanger tube, the outercylindrical sleeve surrounds the inner cylindrical sleeve and the innerdiameter surface of the outer cylindrical sleeve is in contact with theouter diameter surface of the inner cylindrical sleeve.
 38. The methodclaim 36, wherein the step of providing the heat exchanger tubeincludes: arranging the inner portion of the heat exchanger tube to actas a sacrificial anode in the presence of the ice slurry mixture wherebythe inner portion of the heat exchanger tube reduces wear of a portionof the means for moving the ice slurry mixture.
 39. The method of claim36, wherein: the first material composition is a copper based material.40. The method of claim 36, wherein: the second material composition isone from the group consisting of carbon steel, austenitic stainlesssteel, martensitic stainless steel, and aluminum.
 41. A method fordecreasing wear of drive components in an orbital rod heat exchanger,the method comprising: providing a heat exchanger tube with an innerportion of the heat exchanger tube formed from a first materialcomposition and an outer portion of the heat exchanger tube formed froma second material composition, the first material composition being thedifferent from the second material composition whereby the inner portionis in contact with a feed solution flowing through the heat exchangertube and the inner portion has a lower galvanic potential compared tothe drive components when in the presence of the feed solution.
 42. Themethod of claim 41, wherein: the first material composition is acopper-based material.
 43. The method of claim 41, wherein: the secondmaterial composition is one from the group consisting of carbon steel,austenitic stainless steel, martensitic stainless steel, and aluminum.